The present invention relates to a panchromatic microcapsule imaging system which is useful in forming full color images using the imaging processes described in U.S. Pat. Nos. 4,399,209 and 4,440,846 to The Mead Corporation. More particularly, the present invention relates to a panchromatic imaging material employing one or more layers of photosensitive microcapsules and a color correction dye. The microcapsules include three or more sets of microcapsules for different colors whereas the color correction dye absorbs light of a certain wavelength band to which at least one of the different sets of microcapsules is sensitive. The color correction dye is incorporated in a binder present in the one or more layers of microcapsules or in a separate layer, thereby reducing the film speed of at least one of the different sets of microcapsules such that the imaging material exhibits improved gray scale.
U.S. Pat. No. 4,842,976 to The Mead Corporation describes a photosensitive material useful in full color and panchromatic imaging, comprising a support having on its surface a layer of microcapsules. The microcapsules individually contain cyan, magenta and yellow color formers and photosensitive compositions having distinctly different sensitivities in a visible region. More particularly, the photosensitive composition encapsulated with the cyan color former is sensitive to red light, the photosensitive composition encapsulated with the magenta color former is sensitive to green light, and the photosensitive composition encapsulated with the yellow color former is sensitive to blue light. A uniform mixture of the microcapsules is distributed over the surface of the support. The photosensitive material is image-wise exposed to visible light, and thereafter, it is subjected to a uniform rupturing force, such as pressure, which causes the microcapsules in the underexposed and unexposed areas to rupture and release the color formers. The color formers then react with a developer material which is present on the same support or on a different support and produces a full color image.
Distinctively different sensitivities of photosensitive microcapsules are principally enabled by encapsulating with the color formers different photoinitiators as respective constituents of the photosensitive compositions. However, these different photoinitiators often induce difference in film speed between microcapsules for different colors. This difference can be a critical drawback, particularly, in panchromatic imaging since it can result in images with poor gray scale. To compensate difference in film speed and to thereby form images with good gray scale, optical filters must be used upon exposure. Alternatively, it is necessary to separate the red, green blue components of the original, and the intensity of or exposure time for each component must be adjusted in accordance with the film speed of microcapsules for the complementary color.
Addition of radiation absorbers or dyes to adjust photographic properties of an imaging system is known in the art.
U.S. Pat. No. 4,840,866 to the Mead Corporation discloses a microcapsule imaging system which employs a radiation absorber. In this system, the radiation absorber is incorporated i the internal phase of at least one of two sets of microcapsules for the same color to control gamma and dynamic range. Control of these photographic properties is possible using this technique during preparation of microcapsules.
U.S. Pat. No. 4,576,891 to the Mead Corporation discloses a full color and panchromatic microcapusle imaging system which utilizes a dye. According to this patent, the dye can be contained, to prevent cross-talk between microcapsules for different colors, in a binder for microcapsules, in the internal phase of microcapsules or in the walls of microcapsules.